冀北地区早三叠世劈柴拌组火山活动的时代归属及意义  

The Chronological Attribution and Significance of Volcanic Activity of the Early Triassic Pichaiban Formation in Northern Hebei

作　　者：吴江宇 王金贵 张鑫全 梁贤 刘蓓蓓 季虹 陈圆圆 WU Jiang-yu;WANG Jin-gui;ZHANG Xin-quan;LIANG Xian;LIU Bei-bei;JI Hong;CHEN Yuan-yuan(Regional Geological Survey Institute of Hebei Province,Langfang 065000,China;Hebei GEO University,Shijiazhuang 050031,China)

机构地区：[1]河北省区域地质调查院,河北廊坊065000 [2]河北地质大学,河北石家庄05003

出　　处：《河北地质大学学报》2021年第2期19-25,共7页Journal of Hebei Geo University

基　　金：中国地质调查局综合研究项目《中国区域地质志·河北志》(编号:121201091103);河北省地矿局综合研究项目《河北省区域地质调查工作总结研究》(编号:201821)。

摘　　要：通过野外调查,根据岩石组合、岩石成因、接触关系、岩石变质特征及同位素测年资料,将冀北地区劈柴拌组的时代归属于早三叠世,确定了该区存在较强烈火山活动,劈柴拌组为一套浅变质的陆相火山—沉积建造,根据岩石组合特征和接触关系可分为两个岩性段。火山岩岩石地球化学特征显示以钙碱性系列的岩石为主,碱性系列次之,稀土元素总量平均为133.24×10^(-6);δEu平均为0.86,显示轻稀土较富集,轻稀土与重稀土分馏较强,具有壳幔混源岩浆的特征,Th、K、La、Hf、Y元素富集,U、Nb、P、Ti元素亏损,为典型的岩浆弧带岩浆岩。综合河北志(2017)早三叠世侵入岩分析,认为劈柴拌组的火山岩形成于早三叠世后碰撞挤压造山阶段的构造环境。将劈柴拌组厘定为早三叠世,填补了冀北地区早三叠世较强烈火山活动的空白,进一步丰富了印支期中期后碰撞过程中的岩浆活动,补充完善了早三叠世的岩石地层序列。Based on the field investigation,rock association,petrogenesis,contact relationship,metamorphic characteristics and isotopic dating data,the age of the Pichaiba formation in northern Hebei is assigned to the Early Triassic.It is confirmed that there is strong volcanic activity in the area.The Pichaiba formation is a set of shallow metamorphic continental volcanic sedimentary formation.According to the characteristics of rock association and contact relationship,it can be divided into two lithologic sections.The geochemical characteristics of the volcanic rocks show that the calc alkaline series are the main rocks,followed by the alkaline series,and the total REE is 133.24×10^(-6) on average,theδEu value is 0.86 on average,which shows that the LREE is relatively rich,and the LREE and HREE fractionation is strong,with the characteristics of crust mantle mixed magma.The Th,K,La,Hf,Y elements are enriched,U,Nb,P,Ti elements are depleted,which is a typical magma arc zone magmatic rock.Based on the analysis of intrusive rocks of the Early Triassic in The Regional Geology of China,Hebei Province(2017),it is believed that the volcanic rocks of the Pichaiban Formation were formed in the tectonic setting of the post collision compressional orogenic stage in Early Triassic.In this paper,the Pichaiban Formation is determined to be the Early Triassic,which fills the gap of the strong volcanic activity in the Early Triassic in northern Hebei,further enriches the magmatic activity during the post collision process of the Middle Indo-Chinese,and improved the lithostratigraphic sequence of the Early Triassic.

关 键 词：冀北地区 早三叠世 劈柴拌组 钙碱性-碱性火山岩 后碰撞 

分 类 号：P595[天文地球—地球化学]